In recent years, hybrid vehicles having both an internal combustion engine and a motor as a rotating electrical machine mounted thereon as a driving force source, electric vehicles having only a rotating electrical machine mounted thereon as a driving force source, etc. are known in the art.
In drive devices for such vehicles, an oil pressure is typically generated by an oil pump, so that oil for lubrication is supplied to each gear mechanism forming a powder distribution mechanism, a speed reduction mechanism, etc., and oil for lubrication or cooling is supplied to the rotating electrical machine. If the oil for lubrication is not sufficiently supplied to each gear mechanism in such drive devices, bearings etc. may be seized up by friction heat generated by rotation, or the tooth surfaces of each gear may be worn. If the oil for lubrication is excessively supplied to each gear mechanism, loss may be increased which is caused by the gear mechanism stirring oil when it rotates. It is therefore desirable to supply an appropriate amount of lubrication oil to each gear mechanism. The amount of heat that is generated by the rotating electrical machine varies according to the operating state. If oil supply is not sufficient in a situation where the rotating electrical machine generates a large amount of heat, the rotating electrical machine may not be sufficiently cooled by the oil and may be overheated. On the other hand, if a large amount of oil is supplied in a situation where the rotating electrical machine generates a small amount of heat, loss may be excessively increased which is caused by a rotor stirring oil when it rotates. It is therefore desirable to supply an appropriate amount of oil to the rotating electrical machine as well.
Such a technique as in Patent Document 1 is proposed as a technique that improves cooling capability of a rotating electrical machine while reducing loss that is caused by the rotating electrical machine stirring oil. In the technique of Patent Document 1, a relief valve is provided in a main passage that supplies oil from an oil pump to rotating electrical machines, a reduction gear, a power distribution integrating mechanism, etc., and a solenoid valve that is opened and closed according to the temperature of the rotating electrical machines is provided in a return passage between the relief valve and an oil pan. The relief valve returns a part of oil to the oil pan via the return passage if the amount of oil discharged from the oil pump that is driven by an internal combustion engine becomes equal to or larger than a certain amount. In the technique of Patent Document 1, when the temperature of the rotating electrical machines is low, the solenoid valve is opened in order to prioritize reduction in stirring loss, thereby reducing the amount of oil that is supplied to the rotating electrical machines, the reduction gear, the power distribution integrating mechanism, etc. via the main passage. On the other hand, when the temperature of the rotating electrical machines is high, the solenoid valve is closed in order to prioritize cooling of the rotating electrical machines, thereby increasing the amount of oil that is supplied to the rotating electrical machines, the reduction gear, the power distribution integrating mechanism, etc. via the main passage. In the technique of Patent Document 1, opening and closing of the solenoid valve is controlled based on the temperature, and whether the relief valve can be operated or not is controlled according to the state of the solenoid valve. This can reduce an operation set pressure for the relief valve, and can reduce the amount of oil that is supplied from the oil pump to the power distribution integrating mechanism and the reduction gear in the state where cooling of the rotating electrical machine is not required, whereby stirring loss of the power distribution integrating mechanism and the reduction gear can be reduced.
In the technique of Patent Document 1, however, temperature detection sensors for the rotating electrical machines are required, whether or not the temperature of the rotating electrical machines detected by the temperature sensors is equal to or lower than a preset valve opening temperature need be determined, and the operation of opening or closing the solenoid valve need be performed according to the determination result. The device configuration is therefore relatively complicated.